Hybrid Multi-Wavelength Source and Associated Methods

ABSTRACT

A substrate includes a first area in which a laser array chip is disposed. The substrate includes a second area in which a planar lightwave circuit is disposed. The second area is elevated relative to the first area. A trench is formed in the substrate between the first area and the second area. The substrate includes a third area in which an optical fiber alignment device is disposed. The third area is located next to and at a lower elevation than the second area within the substrate. The planar lightwave circuit has optical inputs facing toward and aligned with respective optical outputs of the laser array chip. The planar lightwave circuit has optical outputs facing toward the third area. The optical fiber alignment device is configured to receive optical fibers such that optical cores of the optical fibers respectively align with the optical outputs of the planar lightwave circuit.

CLAIM OF PRIORITY

This application claims priority under 35 U.S.C. 119(e) to U.S.Provisional Patent Application No. 62/873,429, filed Jul. 12, 2019, thedisclosure of which is incorporated herein by reference in its entiretyfor all purposes.

BACKGROUND

Optical data communication systems operate by modulating laser light toencode digital data patterns. The modulated laser light is transmittedthrough an optical data network from a sending node to a receiving node.The modulated laser light having arrived at the receiving node isde-modulated to obtain the original digital data patterns. Therefore,implementation and operation of optical data communication systems isdependent upon having reliable and efficient laser light sources. Also,it is desirable for the laser light sources of optical datacommunication systems to have a minimal form factor and be designed asefficiently as possible with regard to expense and energy consumption.It is within this context that the present invention arises.

SUMMARY

In an example embodiments, a multi-wavelength source is disclosed. Themulti-wavelength source includes a substrate that includes a first areafor receiving a chip and a second area elevated relative to the firstarea. The second area is separated from the first area by a trenchhaving a bottom at a lower elevation within the substrate than the firstarea. The substrate also includes a third area next to the second area.The third area has a lower elevation within the substrate than thesecond area. The multi-wavelength source also includes a laser arraychip disposed in the first area. The laser array chip has opticaloutputs facing toward the second area. The multi-wavelength sourced alsoincludes a planar lightwave circuit disposed in the second area. Theplanar lightwave circuit has optical inputs facing toward and alignedwith respective optical outputs of the laser array chip. The planarlightwave circuit has optical outputs facing toward the third area. Themulti-wavelength sourced also includes an optical fiber alignment devicedisposed in the third area. The optical fiber alignment device isconfigured to receive a number of optical fibers such that optical coresof the number of optical fibers respectively align with the opticaloutputs of the planar lightwave circuit.

In an example embodiments, a method is disclosed for manufacturing amulti-wavelength source. The method includes forming a substrate toinclude a first area for receiving a chip. The method also includesforming the substrate to include a second area elevated relative to thefirst area. The method also includes forming the substrate to include atrench between the first area and the second area. The trench having abottom at a lower elevation within the substrate than the first area.The method also includes forming the substrate to include a third areanext to the second area. The third area has a lower elevation within thesubstrate than the second area. The method also includes disposing alaser array chip in the first area, such that optical outputs of thelaser array chip face toward the second area. The method also includesdisposing a planar lightwave circuit in the second area, such thatoptical inputs of the planar lightwave circuit face toward and alignwith respective optical outputs of the laser array chip, and such thatoptical outputs of the planar lightwave circuit face toward the thirdarea. The method also includes disposing an optical fiber alignmentdevice in the third area. The optical fiber alignment device isconfigured to receive a number of optical fibers such that optical coresof the number of optical fibers respectively align with the opticaloutputs of the planar lightwave circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a top view of an example hybrid MWS, in accordance withsome embodiments of the present invention.

FIG. 1B shows a vertical cross-section view of the example hybrid MWS,referenced as View A-A in FIG. 1A, in accordance with some embodimentsof the present invention.

FIG. 1C shows a more detailed top view arrangement of the laser arraychip and the PLC, in accordance with some embodiments.

FIG. 1D shows a side view of the laser array chip as seen from theperspective of the PLC, referenced as View B-B in FIG. 1C, in accordancewith some embodiments.

FIG. 1E shows a side view of the PLC as seen from the perspective of thelaser chip array, referenced as View C-C in FIG. 1C, in accordance withsome embodiments.

FIG. 1F shows an alternate embodiment of the hybrid MWS in whichdiscrete lasers are disposed on the substrate, rather than having thelasers integrally formed within the laser array chip, in accordance withsome embodiments.

FIG. 2A-1 shows a top view of the substrate, in accordance with someembodiments.

FIG. 2A-2 shows a vertical cross-section view of the substrate,referenced as View A-A in FIG. 2A-1, in accordance with someembodiments.

FIG. 2B-1 shows a top view of the BGA disposed on the substrate, inaccordance with some embodiments.

FIG. 2B-2 shows a vertical cross-section view of the BGA disposed on thesubstrate, referenced as View A-A in FIG. 2B-1, in accordance with someembodiments.

FIG. 2C-1 shows a top view of the laser array chip disposed on the BGA,in accordance with some embodiments.

FIG. 2C-2 shows a vertical cross-section view of the laser array chipdisposed on the BGA, referenced as View A-A in FIG. 2C-1, in accordancewith some embodiments.

FIG. 2D shows a vertical cross-section view of the underfill epoxydisposed between the laser array chip and the substrate and between thesolder balls of the BGA, referenced as View A-A in FIG. 2C-1, inaccordance with some embodiments.

FIG. 2E-1 shows a top view of the PLC disposed on the substrate, inaccordance with some embodiments.

FIG. 2E-2 shows a vertical cross-section view of the PLC disposed on thesubstrate, referenced as View A-A in FIG. 2E-1, in accordance with someembodiments.

FIG. 2F shows a vertical cross-section view of the optical index-matchedepoxy disposed between the PLC and the substrate, referenced as View A-Ain FIG. 2E-1, in accordance with some embodiments.

FIG. 2G-1 shows a top view of the optical fiber alignment devicedisposed on the substrate, in accordance with some embodiments.

FIG. 2G-2 shows a vertical cross-section view of the optical fiberalignment device disposed on the substrate, referenced as View A-A inFIG. 2G-1, in accordance with some embodiments.

FIG. 2H shows a vertical cross-section view of the optical index-matchedepoxy disposed between the optical fiber alignment device and thesubstrate, referenced as View A-A in FIG. 2G-1, in accordance with someembodiments.

FIG. 2I-1 shows a top view of the stiffener structure disposed on thesubstrate, in accordance with some embodiments.

FIG. 2I-2 shows a vertical cross-section view of the stiffener structuredisposed on the substrate, referenced as View A-A in FIG. 2I-1, inaccordance with some embodiments.

FIG. 2J-1 shows a top view of the TIM disposed on the stiffenerstructure, the laser array chip, and the PLC, in accordance with someembodiments.

FIG. 2J-2 shows a vertical cross-section view of the TIM disposed on thestiffener structure, the laser array chip, and the PLC, referenced asView A-A in FIG. 2J-1, in accordance with some embodiments.

FIG. 3 shows a flowchart of a method for manufacturing the hybrid MWS,in accordance with some embodiments.

FIG. 4 shows a diagram of the hybrid MWS indicating where optical lossesoccur, in accordance with some embodiments.

FIG. 5 shows a modified laser array chip coupled to the PLC, inaccordance with some embodiments.

FIG. 6 shows a modified hybrid MWS, in accordance with some embodiments.

FIG. 7 shows the modified hybrid MWS implemented within a pre-amplifiedreceiver, in accordance with some embodiments.

FIG. 8 shows a modified hybrid MWS that includes the modified laserarray chip of FIG. 5 and optical fiber interfaces for the optical inputsand optical outputs of the PLC, in accordance with some embodiments.

FIG. 9 shows a modified hybrid MWS that includes implementation of thePLC in conjunction with a praseodymium-doped fiber amplifier (PDFA) anda 1×M optical splitter, in accordance with some embodiments.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention. Itwill be apparent, however, to one skilled in the art that the presentinvention may be practiced without some or all of these specificdetails. In other instances, well known process operations have not beendescribed in detail in order not to unnecessarily obscure the presentinvention.

Various embodiments of a hybrid multi-wavelength source (MWS) andassociated methods are disclosed herein. The hybrid MWS is designed andconfigured to supply continuous wave (CW) laser light having multiplewavelengths. In some embodiments, the hybrid MWS is a device that emitsmultiple wavelengths of CW laser light that are usable in awavelength-division multiplexing (WDM) system for transmission into asingle optical fiber. Hybrid integration of the MWS disclosed hereinrefers to combining different devices made on separate substrates into asingle package.

It should be understood that the term “wavelength” as used herein refersto the wavelength of electromagnetic radiation. And, the term “light” asused herein refers to electromagnetic radiation within a portion of theelectromagnetic spectrum that is usable by optical data communicationsystems. In some embodiments, the portion of the electromagneticspectrum includes light having wavelengths within a range extending fromabout 1100 nanometers to about 1565 nanometers (covering from the O-Bandto the C-Band, inclusively, of the electromagnetic spectrum). However,it should be understood that the portion of the electromagnetic spectrumas referred to herein can include light having wavelengths either lessthan 1100 nanometers or greater than 1565 nanometers, so long as thelight is usable by an optical data communication system for encoding,transmission, and decoding of digital data throughmodulation/de-modulation of the light. In some embodiments, the lightused in optical data communication systems has wavelengths in thenear-infrared portion of the electromagnetic spectrum. Also, the term“laser beam” as used herein refers to a beam of CW light generated by alaser device. It should be understood that a laser beam may be confinedto propagate in an optical waveguide, such as (but not limited to) anoptical fiber or an optical waveguide within a planar lightwave circuit(PLC). In some embodiments, the laser beam is polarized. And, in someembodiments, the light of a given laser beam has a single wavelength,where the single wavelength can refer to either essentially onewavelength or can refer to a narrow band of wavelengths that can beidentified and processed by an optical data communication system as ifit were a single wavelength.

FIG. 1A shows a top view of an example hybrid MWS 100, in accordancewith some embodiments of the present invention. FIG. 1B shows a verticalcross-section view of the example hybrid MWS 100, referenced as View A-Ain FIG. 1A, in accordance with some embodiments of the presentinvention. The hybrid MWS 100 includes a substrate 101, a laser arraychip 103, a PLC 105, and an optical fiber alignment device 107. Thesubstrate 101 includes a first area 101A for receiving the laser arraychip 103. The substrate 101 also includes a second area 101B elevatedrelative to the first area 101A. The second area 101B is separated fromthe first area 101A by a trench 102 that has a bottom surface at a lowerelevation within the substrate 101 than the first area 101A. Thesubstrate 101 includes a third area 101C next to the second area 101B.The third area 101C has a lower elevation within the substrate 101 thanthe second area 101B.

The laser array chip 103 is disposed in the first area 101A. In someembodiments, the laser array chip 103 is an InP chip. However, in otherembodiments, the laser array chip 103 is a chip other than InP. Thelaser array chip 103 has optical outputs facing toward the second area101B. The PLC 105 is disposed in the second area 101B. The PLC 105 hasoptical inputs facing toward and aligned with respective optical outputsof the laser array chip 103. The PLC 105 has optical outputs facingtoward the third area 101C. The optical fiber alignment device 107 isdisposed in the third area 101C. The optical fiber alignment device 107is configured to receive a number of optical fibers 151, such thatoptical cores of the number of optical fibers 151 respectively alignwith the optical outputs of the PLC 105.

In some embodiments, the laser array chip 103 is attached to thesubstrate 101 by flip-chip bonding, which includes disposing a ball gridarray (BGA) 109 between the laser array chip 103 and respectiveconductive pads exposed on the substrate 101 surface. The BGA 109provides for electrical connectivity between electrical circuitry in thelaser array chip 103 and electrical circuitry within the substrate 101.In some embodiments, the substrate 101 includes a plurality ofelectrically conductive structures electrically connected to a pluralityof electrically conductive pads exposed within the first area 101A ofthe substrate 101. The plurality of electrically conductive pads isconfigured to receive the BGA 109. In some embodiments an epoxyunderfill material 111 is disposed within the first area 101A betweenthe laser array chip 103 and the substrate 101, and between solder ballsof the BGA 109. In some embodiments, the trench 102 within the substrate101 is configured to facilitate deposition of the epoxy underfillmaterial 111. It should be understood that flip-chip attachment of thelaser array chip 103 to the substrate 101 using the BGA 109 is one ofmany different ways that the laser array chip 103 can be attached to thesubstrate 101 and electrically connected to circuitry within thesubstrate 101. In other embodiments, the laser array chip 103 isattached to the substrate 101 using essentially any known electronicpackaging process, which can optionally include disposition of bumps,solder, under-fill, and/or other component(s), between the laser arraychip 103 and the substrate 101, and can include bonding techniques suchas mass reflow, thermal-compression bonding (TCB), wire-bonding, oressentially any other suitable bonding technique. For example, in someembodiments, instead of using the BGA 109, the laser array chip 103 isattached to the substrate 101 using controlled collapse chip connectionbumps.

The PLC 105 and the optical fiber alignment device 107 are attached tothe substrate 101 by an optical index-matched epoxy material 113, suchthat a layer of the optical index-matched epoxy material 113 existsbetween the substrate 101 and each of the PLC 105 and the optical fiberalignment device 107. The optical index-matched epoxy material 113 hasan optical index of refraction that is substantially the same as anoptical index of refraction of optical waveguides within the PLC 105 andlaser array chip 103. Also, in some embodiments, the opticalindex-matched epoxy material 113 has an optical index of refraction thatis substantially the same as an optical index of refraction of opticalcores of the optical fibers 151. In some embodiments, the opticalindex-matched epoxy material 113 is disposed to fill the trench 102within the substrate 101. In some embodiments, the laser array chip 103is slightly spaced apart from the PLC 105, such that the opticalindex-matched epoxy material 113 is disposed within a gap between thelaser array chip 103 and the PLC 105. Also, in some embodiments, the PLC105 is slightly spaced apart from the optical fibers 151 secured withinthe optical fiber alignment device 107, such that the opticalindex-matched epoxy material 113 is disposed within a gap between thePLC 105 and the optical cores of the optical fibers 151. And, morespecifically, the optical index-matched epoxy material 113 is disposedwithin a gap between the PLC 105 and the optical fiber alignment device107.

In some embodiments, a stiffener structure 115 is disposed on thesubstrate 101 to extend around a union of the first area 101A and thesecond area 101B of the substrate 101, without encroaching within thethird area 101C of the substrate. In some embodiments, the stiffenerstructure 115 has a top surface at a substantially same elevation abovethe substrate 101 as a top surface of the laser array chip 103. However,in some embodiments, the top surface of the stiffener structure 115 andthe top surface of the laser array chip 103 are at different elevationsabove the substrate 101. In various embodiments, the stiffener structure115 is formed of a rigid material, such as aluminum or some othermaterial that is chemically, thermally, and mechanically compatible withthe interfacing materials of the hybrid MWS 100. In various embodiments,the stiffener structure 115 is attached to the substrate 101 using anadhesive material, such as an epoxy material. Also, in some embodiments,a thermal interface material (TIM) 117 is disposed across top surfacesof the stiffener structure 115, the laser array chip 103, and the PLC105. In some embodiments, the TIM 117 is a thermal adhesive. In someembodiments, the TIM 117 is Master Bond EP30TC by Master Bond Inc. Insome embodiments, the TIM 117 is a metal or metal alloy, such as Indium(In), Indium-Lead (InPb), among other materials. It should be understoodthat in various embodiments, the TIM 117 is essentially any adhesivethermal interface material that is used in semiconductor packaging toenhance thermal coupling between components. Also, in some embodiments,a lid structure 119 is disposed on the TIM 117. The lid structure 117 isconfigured to cover the laser array chip 103 and the PLC 105. The lidstructure 117 is also configured to extend over the stiffener structure115. In various embodiments, the lid structure 117 is formed of a highthermal conductivity material, such as copper, or aluminum, or copperalloy, or aluminum alloy, among others.

FIG. 1C shows a more detailed top view arrangement of the laser arraychip 103 and the PLC 105, in accordance with some embodiments. FIG. 1Dshows a side view of the laser array chip 103 as seen from theperspective of the PLC 105, referenced as View B-B in FIG. 1C, inaccordance with some embodiments. FIG. 1E shows a side view of the PLC105 as seen from the perspective of the laser chip array 103, referencedas View C-C in FIG. 1C, in accordance with some embodiments. The laserarray chip 103 is configured to generate and output a plurality of laserbeams, i.e., (N) laser beams. In some embodiments, (N) is eight.However, in other embodiments, (N) can be either less than eight orgreater than eight. The plurality of laser beams have differentwavelengths (λ₁-λ_(N)) relative to each other, where the differentwavelengths (λ₁-λ_(N)) are distinguishable to an optical datacommunication system. In some embodiments, the laser array chip 103includes a plurality of lasers DFB-1 to DFB-N for respectivelygenerating the plurality (N) of laser beams, where each laser DFB-1 toDFB-N generates and outputs a laser beam at a respective one of thedifferent wavelengths (λ₁-λ_(N)). Each of the plurality of lasers DFB-1to DFB-N is optically connected to transmit its particular wavelength ofCW laser light to a respective one of the optical outputs L-O1 to L-ONof the laser array chip 103, such that the different wavelengths(λ₁-λ_(N)) of CW laser light generated by the plurality of lasers DFB-1to DFB-N are respectively provided to the different optical output L-O1to L-ON of the laser array chip 103 for transmission from the laserarray chip 103. In some embodiments, each of the plurality of lasersDFB-1 to DFB-N is a distributed feedback laser configured to generate CWlaser light at a particular one of the different wavelengths (λ₁-λ_(N)).The distributed feedback laser is a type of diode laser that has asingle-wavelength emission spectrum or a “single longitudinal mode.” Insome embodiments, the plurality of lasers DFB-1 to DFB-N generate CWlaser light having wavelengths within the O-band, or within a rangeextending from 1260 nanometers to 1330 nanometers. In some embodiments,the distributed feedback of the plurality of lasers DFB-1 to DFB-N iscentered at 1270 nanometers for use with SiGe photodetectors. It shouldbe understood that in other embodiments, any of the plurality of lasersDFB-1 to DFB-N can be configured to generate CW laser light atwavelength(s) of either less than 1260 nanometers or greater than 1330nanometers.

In some embodiments, the PLC 105 includes a dielectric core and claddingin a single layer on a silicon or glass substrate. The PLC 105 includesan interior configuration of optical waveguides configured to routelight received through optical input ports PLC 105 to optical outputports of the PLC 105 in a prescribed manner. In some embodiments, thePLC 105 includes nitride waveguides. However, in other embodiments, thePLC 105 can be implemented using essentially any material that issuitable to form optical waveguides. The PLC 105 is configured toreceive the plurality of laser beams of CW light of the differentwavelengths (λ₁-λ_(N)) from the laser array chip 103 at a correspondingplurality (N) of optical input ports PLC-I1 to PLC-IN of the PLC 105,such that each of the plurality (N) of optical inputs PLC-I1 to PLC-INof the PLC 105 receives a different wavelength of CW laser light.

The PLC 105 is configured to distribute a portion of the CW laser lightreceived at each of the optical inputs PLC-I1 to PLC-IN of the PLC 105to each of a plurality (M) of optical output ports PLC-O1 to PLC-OM ofthe PLC 105, such that the different wavelengths (λ₁-λ_(N)) of CW laserlight received through the plurality (N) of optical inputs of the PLC105 are collectively transmitted through each of the plurality (M) ofoptical outputs PLC-O1 to PLC-ON of the PLC 105. In some embodiments,(M) is sixteen. However, in other embodiments, (M) is either less thansixteen or greater than sixteen. In this manner, the PLC 105 operates todistribute the plurality (N) of laser beams such that all of thedifferent wavelengths (λ₁-λ_(N)) of the plurality (N) of laser beams areprovided to each of the plurality (M) of optical output ports PLC-O1 toPLC-OM of the PLC 105. Therefore, it should be understood that the PLC105 operates to provide light at all of the different wavelengths(λ₁-λ_(N)) of the plurality (N) of laser beams to each one of theoptical output ports PLC-O1 to PLC-OM of the PLC 105. In this manner,the PLC 105 functions as an N×M optical multiplexing device. Also, theoptical power transmitted at a given wavelength through any one of theplurality (M) of optical output ports PLC-O1 to PLC-OM of the PLC 105 isapproximately equal to the optical power received at the givenwavelength through the corresponding one of the optical inputs PLC-I1 toPLC-IN of the PLC 105 divided by (M). Therefore, it should be understoodthat the optical output power of the configuration of the laser arraychip 103 and PLC 105 scales with the number (M) of output channels,rather than with the number (N) of generated CW laser wavelengths. Insome embodiments, the PLC 105 is configured as a star coupler.

The optical fiber alignment device 107 is configured to receive theplurality (M) of optical fibers 151 and respectively align the opticalcores of the plurality (M) of optical fibers 151 to the plurality (M) ofoptical output ports PLC-O1 to PLC-OM of the PLC 105. In someembodiments, the optical fiber alignment device 107 is a v-groove arraythat includes a plurality (M) of v-grooves, where each v-groove isconfigured to receive and align one of the plurality (M) of opticalfibers 151. However, it should be understood that in other embodiments,the optical fiber alignment device 107 can be configured in a mannerthat does not include v-grooves, so long as the optical fiber alignmentdevice 107 is configured to receive the plurality (M) of optical fibers151 and respectively align the optical cores of the plurality (M) ofoptical fibers 151 to the plurality (M) of optical output ports PLC-O1to PLC-OM of the PLC 105. In various embodiments, the optical fiberalignment device 107 is formed of a material that is chemically,thermally, and mechanically compatible with the interfacing materialsand components of the hybrid MWS 100. For example, in some embodiments,the optical fiber alignment device 107 is formed of aluminum, plastic,or another suitable material.

In some embodiments, the laser array chip 103 is secured to thesubstrate 101 before the PLC 105 is secured to the substrate 101. Inthese embodiments, the PLC 105 has to be optically aligned with thelaser array chip 103 so that the plurality of optical input ports PLC-I1to PLC-IN of the PLC 105 respectively optically align with the pluralityof optical output ports L-O1 to L-ON of the laser array chip 103. Insome embodiments, the laser array chip 103 and the PLC 105 arecollectively configured to provide for active alignment of the PLC 105to the laser array chip 103 through operation of the laser array chip103 after the laser array chip 103 is disposed in the first area 101A ofthe substrate 101. In some embodiments, the laser array chip 103includes a first alignment laser DFB-A1 configured and connected toprovide CW laser light to a first alignment optical output L-AO1 on thelaser array chip 103. The first alignment optical output L-AO1 facestoward the second area 101B of the substrate 101 when the laser arraychip 103 is attached to the substrate 101 within the first area 101A ofthe substrate 101. In some embodiments, the first alignment opticaloutput L-AO1 is positioned at a first side of the plurality (N) oflasers DFB-1 to DFB-N, such as shown in FIG. 1C. The laser array chip103 also includes a first alignment photodetector PD-A1 opticallyconnected to a first alignment optical input L-AI1 on the laser arraychip 103. The first alignment optical input L-AI1 faces toward thesecond area 101B of the substrate 101 when the laser array chip 103 isattached to the substrate 101 within the first area 101A of thesubstrate 101. In some embodiments, the first alignment optical inputL-AI1 is positioned next to the first alignment optical output L-AO1,such as shown in FIG. 1D.

The PLC 105 includes a first alignment waveguide WG-1 configured toextend from a first alignment optical input PLC-AI1 on the PLC 105 to afirst alignment optical output PLC-AO1 on the PLC 105, such that lightentering the first alignment optical input PLC-AI1 on the PLC 105 isconveyed through the first alignment waveguide WG-1 and through thefirst alignment optical output PLC-AO1 on the PLC 105. The PLC 105 isconfigured so that both the first alignment optical input PLC-AI1 andthe first alignment optical output PLC-AO1 of the PLC 105 face towardthe first area 101A when the PLC 105 is positioned within the secondarea 101B on the substrate 101. The PLC 105 is properly aligned with thelaser array chip 103 when the first alignment optical input PLC-AI1 ofthe PLC 105 is optically aligned with the first alignment optical outputL-AO1 of the laser array chip 103, and when the first alignment opticaloutput PLC-AO1 of the PLC 105 is optically aligned with the firstalignment optical input L-AI1 of the laser array chip 103, such that CWlaser light transmitted from the first alignment laser DFB-A1 travelsthrough the first alignment waveguide WG-1 and back into the laser arraychip 103 for detection by the first alignment photodetector PD-A1. Inthis manner, during active alignment of the PLC 105 to the laser arraychip 103, the laser array chip 103 is operated so that the firstalignment laser DFB-A1 operates to transmit CW laser light through thefirst alignment optical output L-AO1, while the first alignmentphotodetector PD-A1 operates to detect light received through the firstalignment optical input L-AI1. Detection of light by the first alignmentphotodetector PD-A1 indicates that the PLC 105 is properly aligned withthe laser chip array 103.

In some embodiments, to provide for even better optical alignmentbetween the PLC 105 and the laser array chip 103, the laser array chip103 includes a second alignment laser DFB-A2 configured and connected toprovide CW laser light to a second alignment optical output L-AO2 on thelaser array chip 103. The second alignment optical output L-AO2 facestoward the second area 101B of the substrate 101 when the laser arraychip 103 is attached to the substrate 101 within the first area 101A ofthe substrate 101. In some embodiments, the second alignment opticaloutput L-A2 is positioned at a second side of the plurality (N) oflasers DFB-1 to DFB-N, such as shown in FIG. 1C. The laser array chip103 also includes a second alignment photodetector PD-A2 opticallyconnected to a second alignment optical input L-A12 on the laser arraychip 103. The second alignment optical input L-A12 faces toward thesecond area 101B of the substrate 101 when the laser array chip 103 isattached to the substrate 101 within the first area 101A of thesubstrate 101. In some embodiments, the second alignment optical inputL-A12 is positioned next to the second alignment optical output L-AO2,such as shown in FIG. 1D.

The PLC 105 includes a second alignment waveguide WG-2 configured toextend from a second alignment optical input PLC-A12 on the PLC 105 to asecond alignment optical output PLC-AO2 on the PLC 105, such that lightentering the second alignment optical input PLC-A12 on the PLC 105 isconveyed through the second alignment waveguide WG-2 and through thesecond alignment optical output PLC-AO2 on the PLC 105. The PLC 105 isconfigured so that both the second alignment optical input PLC-A12 andthe second alignment optical output PLC-AO2 of the PLC 105 face towardthe first area 101A when the PLC 105 is positioned within the secondarea 101B on the substrate 101. The PLC 105 is properly aligned with thelaser array chip 103 when the second alignment optical input PLC-A2 ofthe PLC 105 is optically aligned with the second alignment opticaloutput L-AO2 of the laser array chip 103, and when the second alignmentoptical output PLC-AO2 of the PLC 105 is optically aligned with thesecond alignment optical input L-A2 of the laser array chip 103, suchthat CW laser light transmitted from the second alignment laser DFB-A2travels through the second alignment waveguide WG-2 and back into thelaser array chip 103 for detection by the second alignment photodetectorPD-A2. In this manner, during active alignment of the PLC 105 to thelaser array chip 103, the laser array chip 103 is operated so that thefirst alignment laser DFB-A1 operates to transmit CW laser light throughthe first alignment optical output L-AO1, while the first alignmentphotodetector PD-A1 operates to detect light received through the firstalignment optical input L-AI1. Also, the laser array chip 103 isoperated so that the second alignment laser DFB-A2 operates to transmitCW laser light through the second alignment optical output L-AO2, whilethe second alignment photodetector PD-A2 operates to detect lightreceived through the second alignment optical input L-A2. Detection oflight by both the first alignment photodetector PD-A1 and the secondalignment photodetector PD-A2 indicates that the PLC 105 is properlyaligned with the laser chip array 103. Detection of strong photocurrentsignals by both the first alignment photodetector PD-A1 and the secondalignment photodetector PD-A2 indicates that the PLC 105 is properlyaligned with the laser chip array 103 with respect to coordinates in thex, y, and z directions, and with respect to roll in the y-z plane, yawin the x-y plane, and pitch in the x-z plane.

FIG. 1F shows an alternate embodiment of the hybrid MWS 100 in whichdiscrete lasers DFB-1 to DFB-N are disposed on the substrate 101, ratherthan having the lasers DFB-1 to DFB-N integrally formed within the laserarray chip 103, in accordance with some embodiments. The configurationof FIG. 1F is the same as that of FIG. 1C, with the exception of havingdiscrete lasers DFB-1 to DFB-N instead of the laser array chip 103.Also, in the embodiment of FIG. 1F, if the integrated active alignmentbetween the PLC 105 and the lasers DFB-1 to DFB-N is implemented, thenthe alignment lasers DFB-A1 and DFB-A2 will also be discretely disposedon the substrate 101, and the alignment photodetectors PD-A1 and PD-A2will also be discretely disposed on the substrate 101. In thisembodiment, the position and orientation on the substrate 101 of eachdiscrete laser DFB-1 to DFB-N is carefully controlled. Also, theposition and orientation on the substrate 101 of each discrete alignmentlaser DFB-A1 and DFB-A2 and each discrete photodetector PD-A1 and PD-A2is carefully controlled. In some embodiments, the substrate 101 isformed to include a number of positioning and aligning structures tofacilitate proper positioning and alignment on the substrate 101 of thelasers DFB-1 to DFB-N, the alignment lasers DFB-A1 and DFB-A2, and thealignment photodetectors PD-A1 and PD-A2.

FIGS. 2A-1 through 2J-2 describe an example assembly process flow formanufacturing the hybrid MWS 100, in accordance with some embodiments.FIG. 2A-1 shows a top view of the substrate 101, in accordance with someembodiments. FIG. 2A-2 shows a vertical cross-section view of thesubstrate 101, referenced as View A-A in FIG. 2A-1, in accordance withsome embodiments. The first area 101A is where the laser array chip 103is to be disposed. The second area 101B is where the PLC 105 is to bedisposed. The third area 101C is where the optical fiber alignmentdevice 107 is to be disposed. The trench 102 is formed between the firstarea 101A and the second area 101B. In some embodiments, the trenchextends along a full length of the side of the laser array chip 103 thatfaces toward the PLC 105, i.e., that faces toward the second area 101B.The bottom of the trench 102 is at a lower elevation with the substrate101 than the first area 101A. Also, the second area 101B is at a higherelevation on the substrate 101 than the first area 101A. It should beunderstood that the second area 101B forms a mesa-like structure uponwhich the PLC 105 is disposed. Also, when the PLC 105 is disposed withinthe second area 101B, a portion of the PLC 105 will extend over andabove a portion of the trench 102, and a portion of the PLC 105 willextend over and above a portion of the third area 101C. Also, theelevation of the third area 101C within the substrate 101 is lower thanthe elevation of the second area 101B.

It should be understood that the specific elevation of the second area101B is set so that the optical inputs PLC-I1 to PLC-IN can be opticallyaligned with the optical outputs L-O1 to L-ON of the laser array chip103. Therefore, the specific elevation of the second area 101B withinthe substrate 101 relative to the first area 101A is dependent upon thespecific configurations of the laser array chip 103 and the PLC 105.Similarly, the specific elevation of the third area 101C is set so thatthe optical cores of the optical fibers 151 can be optically alignedwith the optical outputs PLC-O1 to PLC-OM of the PLC 105 when theoptical fibers 105 are positioned in the optical fiber alignment device107. Therefore, the specific elevation of the third area 101C within thesubstrate 101 relative to the second area 101B is dependent upon thespecific configurations of the PLC 105 and the optical fiber alignmentdevice 107.

The substrate 101 is an electronic packaging substrate. In someembodiments, the substrate 101 is formed of a dielectric material. Insome embodiments, the substrate 101 is formed of an organic material. Insome embodiments, the substrate 101 is formed of a ceramic material. Insome embodiments, the substrate 101 is formed of aluminum oxide (Al₂O₃),or aluminum nitride (AlN), or a similar ceramic material. In someembodiments, the substrate 101 is an Indium-Phosphide (III-V) substrate.It should be understood that in various embodiments, the substrate 101can be formed of essentially any other type of substrate material uponwhich electronic devices and/or optical-electronic devices and/oroptical waveguides and/or optical fiber(s)/fiber ribbon(s) can bemounted. Also, it should be understood that the substrate 101 can beconfigured to include electrical circuitry in the form of conductivelines/structures formed and routed in one or more levels within thesubstrate 101, with conductive lines/structures in different levels ofthe substrate 101 electrically connected by one or more conductive viastructures as needed to form a prescribed electrical circuitconfiguration.

FIG. 2B-1 shows a top view of the BGA 109 disposed on the substrate 101,in accordance with some embodiments. FIG. 2B-2 shows a verticalcross-section view of the BGA 109 disposed on the substrate 101,referenced as View A-A in FIG. 2B-1, in accordance with someembodiments. It should be understood that the particular arrangement ofthe BGA 109 shown in FIGS. 2B-1 and 2B-2 is provided by way of exampleand in no way limits the possible configuration of the BGA 109 invarious embodiments. Also, as previously mentioned, the BGA 109 is oneexample of various possible ways in which the laser array chip 103 canbe physically and electrically connected to the substrate 101.Therefore, it should be understood that while the BGA 109 technique isused in some embodiments, use of the BGA 109 technique is not requiredin all embodiments.

FIG. 2C-1 shows a top view of the laser array chip 103 disposed on theBGA 109, in accordance with some embodiments. FIG. 2C-2 shows a verticalcross-section view of the laser array chip 103 disposed on the BGA 109,referenced as View A-A in FIG. 2C-1, in accordance with someembodiments. In some embodiments, the laser array chip 103 is configuredso that the flip-chip manufacturing technique is utilized to connectedthe laser array chip 103 to the BGA 109 or other connection mechanism.It should be understood that the individual solder balls of the BGA 109are disposed on corresponding exposed electrical pads on the substrate101. Similarly, each solder ball of the BGA 109 also contacts acorresponding exposed electrical pad on the laser array chip 103. Then,when the solder balls of the BGA 109 are reflowed, each solder ball ofthe BGA 109 becomes fused with its corresponding electrical pad on thesubstrate 101 and with its corresponding electrical pad on the laserarray chip 103.

FIG. 2D shows a vertical cross-section view of the underfill epoxy 111disposed between the laser array chip 103 and the substrate 101 andbetween the solder balls of the BGA 109, referenced as View A-A in FIG.2C-1, in accordance with some embodiments. During application of theunderfill epoxy 111, the trench 102 acts as a reservoir to enable thefabricator to control the flow of the underfill epoxy 111.

FIG. 2E-1 shows a top view of the PLC 105 disposed on the substrate 101,in accordance with some embodiments. FIG. 2E-2 shows a verticalcross-section view of the PLC 105 disposed on the substrate 101,referenced as View A-A in FIG. 2E-1, in accordance with someembodiments. In some embodiments, the PLC 105 is positioned on thesubstrate 101 such that a small gap exists between the PLC 105 and thelaser array chip 103. This small gap allows for movement of the PLC 105relative to the laser array chip 103 during the process of activelyaligning the PLC 105 to the laser array chip 103. As previouslydiscussed, the alignment lasers DFB-A1 and/or DFB-A2 along with theircorresponding photodetectors PD-A1 and PD-A2 are operated to activelyalign the PLC 105 to the laser array chip 103. Therefore, at this stageof hybrid MWS 100 assembly process, power is supplied to the laser arraychip 103. In some embodiments, power is supplied to the laser array chip103 through circuitry within the substrate 101. Also, it should beappreciated that by using the integrated alignment lasers DFB-A1 and/orDFB-A2 and the integrated photodetectors PD-A1 and/or PD-A2 on the laserarray chip 103 in conjunction with the loopback alignment waveguidesWG-1 and WG-2 on the PLC 105, it is not necessary for the alignment tool(the tool used to position the PLC 105 on the substrate 101) to have alaser or a photodetector for alignment purposes.

FIG. 2F shows a vertical cross-section view of the optical index-matchedepoxy 113 disposed between the PLC 105 and the substrate 101, referencedas View A-A in FIG. 2E-1, in accordance with some embodiments. In someembodiments, the trench 102 facilitates disposal of the opticalindex-matched epoxy 113 between the PLC 105 and the substrate 101, andbetween the PLC 105 and the laser array chip 103. Also, it should beappreciated that the mesa-like structure corresponding to the secondarea 101B of the substrate 101 serves to reduce a thickness of theoptical index-matched epoxy 113 bond layer between the PLC 105 and thesubstrate 101.

FIG. 2G-1 shows a top view of the optical fiber alignment device 107disposed on the substrate 101, in accordance with some embodiments. FIG.2G-2 shows a vertical cross-section view of the optical fiber alignmentdevice 107 disposed on the substrate 101, referenced as View A-A in FIG.2G-1, in accordance with some embodiments. In some embodiments, theoptical fibers 151 are attached to the optical fiber alignment device107 before the optical fiber alignment device 107 is attached to thesubstrate 101. In these embodiments, one or more of the lasers DFB-1 toDFB-N of the laser array chip 103 can be operated to provide for a lightsource for active alignment of the optical fiber alignment device 107with the PLC 105. In these embodiments, at least some of the opticalfibers 151 attached to the optical fiber alignment device 107 areoptically connected to a photodetector device to provide for detectionof light transmission through the optical fibers 151, which indicatesproper optical alignment of the optical fibers 151 with the opticaloutput ports PLC-O1 to PLC-ON of the PLC 105, which in turn indicatesproper positioning and alignment of the optical fiber alignment device107 relative to the substrate 101. FIG. 2H shows a verticalcross-section view of the optical index-matched epoxy 113 disposedbetween the optical fiber alignment device 107 and the substrate 101,referenced as View A-A in FIG. 2G-1, in accordance with someembodiments.

FIG. 2I-1 shows a top view of the stiffener structure 115 disposed onthe substrate 101, in accordance with some embodiments. FIG. 2I-2 showsa vertical cross-section view of the stiffener structure 115 disposed onthe substrate 101, referenced as View A-A in FIG. 2I-1, in accordancewith some embodiments. An elevation of a top surface of the stiffenerstructure 115 above the substrate 101 is at least as high as anelevation of a top surface of the laser array chip 103 above thesubstrate 101 and an elevation of a top surface of the PLC 105 above thesubstrate 101. The stiffener structure 115 is configured to providerigidity and mechanical strength to the hybrid MWS 100. The stiffenerstructure 115 is also configured to provide a mounting structure for thelid 119. In some embodiments, the stiffener structure 115 is configuredto extend around a union of the first area 101A and the second area 101Bof the substrate 101 without encroaching within the third area 101C ofthe substrate 101.

FIG. 2J-1 shows a top view of the TIM 117 disposed on the stiffenerstructure 115, the laser array chip 103, and the PLC 105, in accordancewith some embodiments. FIG. 2J-2 shows a vertical cross-section view ofthe TIM 117 disposed on the stiffener structure 115, the laser arraychip 103, and the PLC 105, referenced as View A-A in FIG. 2J-1, inaccordance with some embodiments. FIG. 1A shows a top view of the lid119 disposed on the TIM 117, in accordance with some embodiments. FIG.1B shows a vertical cross-section view of the lid 119 disposed on theTIM 117, referenced as View A-A in FIG. 1A, in accordance with someembodiments. In this embodiment, the TIM 117 functions as an adhesive tosecure the lid 119 to the stiffener structure 115, the laser array chip103, and the PLC 105.

FIG. 3 shows a flowchart of a method for manufacturing the hybrid MWS100, in accordance with some embodiments. The method includes anoperation 301 for forming the substrate 101 to include the first area101A for receiving a chip. In some embodiments, the substrate is formedof a dielectric material. In some embodiments, the substrate is formedof a ceramic material. In some embodiments, the substrate is formed ofaluminum oxide, or aluminum nitride, or a similar ceramic material. Themethod also includes an operation 303 for forming the substrate 101 toinclude the second area 101B elevated relative to the first area 101A.The method also includes an operation 305 for forming the substrate 101to include the trench 102 between the first area 101A and the secondarea 101B. The trench 102 has a bottom at a lower elevation within thesubstrate 101 than the first area 101A. In some embodiments, the trench102 is formed to extend along the full length of the side of the laserarray chip 103 that faces toward the PLC 105. The method also includesan operation 307 for forming the substrate 101 to include the third area101C next to the second area 101B. The third area 101C has a lowerelevation within the substrate 101 than the second area 101B. The methodalso includes an operation 309 for disposing the laser array chip 103 inthe first area 101A, such that the optical outputs L-O1 to L-ON of thelaser array chip 103 face toward the second area 101B. The method alsoincludes an operation 311 for disposing the PLC 105 in the second area101B, such that the optical inputs PLC-I1 to PLC-IN of the PLC 105 facetoward and align with respective optical outputs L-O1 to L-ON of thelaser array chip 103, and such that optical outputs PLC-O1 to PLC-OM ofthe PLC 105 face toward the third area 101C. The method also includes anoperation 313 for disposing the optical fiber alignment device 107 inthe third area 101C. The optical fiber alignment device 107 isconfigured to receive the number of optical fibers 151, such thatoptical cores of the number of optical fibers 151 respectively alignwith the optical outputs PLC-O1 to PLC-OM of the PLC 105.

The method also includes positioning the PLC 105 so that the opticalinputs PLC-I1 to PLC-IN of the PLC 105 respectively receive CW laserlight from the optical outputs L-O1 to L-ON of the laser array chip 103,such that each of the optical inputs PLC-I1 to PLC-IN of the PLC 105receives a different wavelength of CW laser light. In some embodiments,the method includes operating the laser array chip 103 to perform activealignment of the PLC 105 to the laser array chip 103 after the laserarray chip 103 is disposed in the first area 101A on the substrate 101and is connected to the substrate 101.

In some embodiments, the method includes operating the first alignmentlaser DFB-A1 on the laser array chip 103 to transmit CW laser lightthrough the first alignment optical output L-AO1 on the laser array chip103. Also, in these embodiments, the method includes operating the firstalignment photodetector PD-A1 on the laser array chip 103 to detect whenthe CW laser light enters the first alignment optical input L-AI1 on thelaser array chip 103, by way of having traveled through the firstalignment waveguide WG-1 on the PLC 105. Also, in these embodiments, themethod includes aligning the PLC 105 on the substrate 101 relative tothe laser array chip 103 so that the CW laser light transmitted throughthe first alignment optical output L-AO1 on the laser array chip 103enters the first alignment optical input PLC-AI1 on the PLC 105 andtravels through the first alignment waveguide WG-1 to exit the firstalignment optical output PLC-AO1 on the PLC 105 and enter the firstalignment optical input L-AI1 on the laser array chip 103 and bedetected by the first alignment photodetector PD-A1.

In some embodiments, the method further includes operating the secondalignment laser DFB-A2 on the laser array chip 103 to transmit CW laserlight through the second alignment optical output L-AO2 on the laserarray chip 103. In these embodiments, the method also includes operatingthe second alignment photodetector PD-A2 to detect when the CW laserlight enters the second alignment optical input L-A2 on the laser arraychip 103. Also, in these embodiments, the method includes aligning thePLC 105 on the substrate 101 relative to the laser array chip 103 sothat the CW laser light transmitted through the second alignment opticaloutput L-AO2 on the laser array chip 103 enters the second alignmentoptical input PLC-A12 on the PLC 105 and travels through the secondalignment waveguide WG-2 to exit the second alignment optical outputPLC-AO2 on the PLC 105 and enter the second alignment optical inputL-A12 on the laser array chip 103 and be detected by the secondalignment photodetector PD-A2.

Also, in some embodiments, the operation 309 for disposing the laserarray chip 103 in the first area 101A of the substrate 101 includesflip-chip connecting of the laser array chip 103 to the substrate 101using the BGA 109 or other connection mechanism. Also, in theseembodiments, the method includes disposing the BGA 109 on the pluralityof electrically conductive pads exposed at the surface of the substrate101. Also, in some embodiments, the method includes disposing the epoxyunderfill material 111 within the first area 101A on the substrate 101between the laser array chip 103 and the substrate 101, and betweensolder balls of the BGA 109. In some embodiments, the method includesusing the trench 102 to facilitate deposition of the epoxy underfillmaterial 111.

Also, in some embodiments, the method includes disposing theindex-matched epoxy material 113 between the PLC 105 and the substrate101. Also, in some embodiments, the method includes disposing theindex-matched epoxy material 113 to fill the trench 102 in the substrate101 and the gap between the laser array chip 103 and the PLC 105. Also,in some embodiments, the method includes disposing the index-matchedepoxy material 113 between the optical fiber alignment device 107 andthe substrate 101. Also, in some embodiments, the method includesdisposing the index-matched epoxy material 113 to fill the gap betweenthe PLC 105 and the optical fiber alignment device 107.

Also, in some embodiments, the method includes attaching the stiffenerstructure 115 to the substrate 101, such that the stiffener structureextends around a union of the first area 101A and the second area 101Bon the substrate 101 without encroaching within the third area 101C onthe substrate 101. Also, in some embodiments, the method includesdisposing the TIM 117 across top surfaces of the stiffener structure115, the laser array chip 103, and the PLC 105. Also, in someembodiments, the method includes positioning the lid structure 119 onthe TIM 117, such that the lid structure 119 covers the laser array chip103 and the PLC 105, and such that the lid structure 119 also extendsover the stiffener structure 115.

FIG. 4 shows a diagram of the hybrid MWS 100 indicating where opticallosses occur, in accordance with some embodiments. For each wavelengthof light generated by a corresponding one of the plurality of lasersDFB-1 to DFB-N in the laser array chip 103, a first optical loss L1occurs at the interface between the laser array chip 103 and the PLC105. In some embodiments, the first optical loss L1 is less than orequal to about 2 dB. For each wavelength of light, a second optical lossL2 occurs as the light travels through the PLC 105 to the plurality (M)of optical outputs PLC-O1 to PLC-OM of the PLC 105. In some embodiments,the second optical loss L2 is less than or equal to about 1.7 dB. Also,for each wavelength of light, a third optical loss L3 occurs at theinterface between the PLC 105 of the optical fiber 151-x. In someembodiments, the third optical loss L3 is less than or equal to about 1dB.

FIG. 5 shows a modified laser array chip 103A coupled to the PLC 105, inaccordance with some embodiments. The modified laser array chip 103Aincludes semiconductor optical amplifiers SOA-1 to SOA-N respectivelydisposed to amplify the CW laser light generated by the lasers DFB-1 toDFB-N. Each of SOA-1 to SOA-N is configured to generate an amplifiedversion of the CW laser light received from the respective one of thelasers DFB-1 to DFB-N and provide the amplified version of the CW laserlight to the respective optical output L-O1 to L-ON of the laser arraychip 103. In various embodiments, the modified laser array chip 103A canbe implemented in the hybrid MWS 100 in place of the laser array chip103.

FIG. 6 shows a modified hybrid MWS 100A, in accordance with someembodiments. The modified hybrid MWS 100A is like the hybrid MWS 100,with the exception that an array of SOAs 148 is disposed between the PLC105 and the optical fibers 151-1 to 151-M, which are attached to theoptical fiber alignment device 107. The array of SOAs 148 includes SOA-1to SOA-M respectively positioned to receive light from the opticaloutputs PLC-O1 to PLC-OM of the PLC 105. Each of SOA-1 to SOA-M isconfigured to amplify the received light and transmit the amplifiedlight into the optical core of the respective one of the optical fibers151-1 to 151-M. The array of SOAs 148 is positioned on the substrate 101and secured to the substrate 101 by the optical index-matched epoxy 113.As compared to the SOA implementation in the modified laser array chip103A of FIG. 5, the array of SOAs 148 provides for separate optimizationof the lasers DFB-1 to DFB-N and the SOA-1 to SOA-N. Also, as comparedto the SOA implementation in the modified laser array chip 103A of FIG.5, the array of SOAs 148 provides more gain from each of SOA-1 to SOA-Nand lower optical insertion loss through the PLC 105.

FIG. 7 shows the modified hybrid MWS 100A implemented within apre-amplified receiver, in accordance with some embodiments. The opticalfibers 151-1 to 151-M are optically connected to respective opticaltransmitters Tx-1 to Tx-M. Each of the optical transmitters Tx-1 to Tx-Mis optically connected to an optical data communication link, asindicated by arrows 157. An array of SOAs 161 is optically connected toreceive the optical signals from the optical transmitters Tx-1 to Tx-M,by way of the optical data communication link, as indicated by arrows158. Each of SOA-1 to SOA-M amplifies the optical signal that itreceives and transmits the amplified optical signal to through arespective optical fiber 163-1 to 163-M to a respective optical receiverRx-1 to Rx-M. Use of the modified hybrid MWS 100A in the pre-amplifiedreceiver of FIG. 7 provides extra gain from the unsaturated array ofSOAs 148 and can improve link margin to +3 dB or better.

FIG. 8 shows a modified hybrid MWS 100B that includes the modified laserarray chip 103A of FIG. 5 and optical fiber interfaces for the opticalinputs and optical outputs of the PLC 105, in accordance with someembodiments. The PLC 105 is disposed on a substrate 181. The substrate181 is disposed on the substrate 101. Respective optical fibers IF-1 toIF-N are secured to the substrate 181 and are respectively opticallyconnected to the optical inputs PLC-I1 to PLC-IN of the PLC 105. Also,respective optical fibers OF-1 to OF-M are secured to the substrate 181and are respectively optically connected to the optical outputs PLC-O1to PLC-OM of the PLC 105. Also, in some embodiments, optical fibersIF-A1 and OF-A1 are optically connected to the first alignment opticalinput PLC-AI1 and the first alignment optical output PLC-AO1 of the PLC105, respectively. The optical fibers IF-A1 and OF-A1 are secured to thesubstrate 181. Also, in some embodiments, optical fibers IF-A2 and OF-A2are optically connected to the second alignment optical input PLC-A12and the second alignment optical output PLC-AO2 of the PLC 105,respectively. The optical fibers IF-A2 and OF-A2 are secured to thesubstrate 181. Use of optical fiber interfaces for the optical inputsand optical outputs of the PLC 105 serve to reduce the optical lossesthrough the PLC 105. Also, use of optical fiber interfaces for theoptical inputs and optical outputs of the PLC 105 makes it easer toimplement optical isolators, if needed.

FIG. 9 shows a modified hybrid MWS 100C that includes implementation ofthe PLC 105 in conjunction with a praseodymium-doped fiber amplifier(PDFA) 174 and a 1×M optical splitter 176, in accordance with someembodiments. The PLC 105 is implemented on a substrate 171. Thesubstrate 171 is attached to the substrate 101. Optical fibers IF-1 toIF-N are optically connected to the optical inputs PLC-I1 to PLC-IN ofthe PLC 105. The optical fibers IF-1 to IF-N are attached to thesubstrate 171. Each optical fiber IF-1 to IF-N receives CW laser lightfrom a respective one of the lasers DFB-1 to DFB-N in the laser arraychip 103. The PLC 105 is implemented with the number (M) of opticaloutputs equal to one. A first end of an optical fiber 173 is opticallyconnected to the optical output PLC-O1 of the PLC 105. A second end ofthe optical fiber 173 is optically connected to an optical input of thePDFA 174. The optical fiber 173 is attached to the substrate 171. Afirst end of an optical fiber 175 is optically connected to an opticaloutput of the PDFA 174. A second end of the optical fiber 175 isoptically connected to an optical input of the 1×M optical splitter 176.The optical fiber 175 is attached to the substrate 171. The number (M)of optical fibers OF-1 to OF-M are respectively optically connected tothe (M) optical outputs of the 1×M optical splitter 176. The opticalfibers OF-1 to OF-M are attached to the substrate 171. The optical coresof the optical fibers 151-1 to 151-M are aligned to optically couplewith the optical cores of the optical fibers OF-1 to OF-M, respectively.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the invention. Individual elements or features ofa particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin other embodiment(s), even if not specifically shown or described. Thesame may also be varied in many ways. Such variations are not to beregarded as a departure from the invention, and all such modificationsare intended to be included within the scope of the invention.

Although the foregoing invention has been described in some detail forpurposes of clarity of understanding, it will be apparent that certainchanges and modifications can be practiced within the scope of theappended claims. Accordingly, the present embodiments are to beconsidered as illustrative and not restrictive, and the invention is notto be limited to the details given herein, but may be modified withinthe scope and equivalents of the described embodiments.

What is claimed is:
 1. A multi-wavelength source, comprising: asubstrate including a first area for receiving a chip and a second areaelevated relative to the first area, the second area separated from thefirst area by a trench having a bottom at a lower elevation within thesubstrate than the first area, the substrate including a third area nextto the second area, the third area having a lower elevation within thesubstrate than the second area; a laser array chip disposed in the firstarea, the laser array chip having optical outputs facing toward thesecond area; a planar lightwave circuit disposed in the second area, theplanar lightwave circuit having optical inputs facing toward and alignedwith respective optical outputs of the laser array chip, the planarlightwave circuit having optical outputs facing toward the third area;and an optical fiber alignment device disposed in the third area, theoptical fiber alignment device configured to receive a number of opticalfibers such that optical cores of the number of optical fibersrespectively align with the optical outputs of the planar lightwavecircuit.
 2. The multi-wavelength source as recited in claim 1, whereinthe substrate is formed of a dielectric material.
 3. Themulti-wavelength source as recited in claim 1, wherein the substrate isformed of aluminum oxide, or aluminum nitride, or a ceramic material. 4.The multi-wavelength source as recited in claim 1, wherein the trenchextends along a full length of a side of the laser array chip that facestoward the planar lightwave circuit.
 5. The multi-wavelength source asrecited in claim 1, wherein the laser array chip includes a number (N)of distributed feedback lasers, wherein N is greater than one, each ofthe number (N) of distributed feedback lasers configured to generate adifferent wavelength of continuous wave laser light, each of the number(N) of distributed feedback lasers optically connected to transmit thedifferent wavelength of continuous wave laser light to a respectiveoptical output of the laser array chip, such that each optical output ofthe laser array chip outputs one unique wavelength of continuous wavelaser light.
 6. The multi-wavelength source as recited in claim 5,wherein the laser array chip includes the number (N) of semiconductoroptical amplifiers respectively optically connected to the number (N) ofdistributed feedback lasers, each of the number (N) of semiconductoroptical amplifiers configured to generate an amplified version of thecontinuous wave laser light received from the respective one of thenumber (N) of distributed feedback lasers and provide the amplifiedversion of the continuous wave laser light to the respective opticaloutput of the laser array chip.
 7. The multi-wavelength source asrecited in claim 5, wherein the planar lightwave circuit has the number(N) of optical inputs positioned to receive continuous wave laser lightfrom the number (N) of optical outputs of the laser array chip, suchthat each of the number (N) of optical inputs of the planar lightwavecircuit receives a different wavelength of continuous wave laser light,the planar lightwave circuit having a number (M) of optical outputs, theplanar lightwave circuit configured to distribute a portion of thecontinuous wave laser light received at each of the optical inputs ofthe planar lightwave circuit to each of the number (M) of opticaloutputs of the planar lightwave circuit, such that the differentwavelengths of continuous wave laser light received through the number(N) of optical inputs of the planar lightwave circuit are collectivelytransmitted through each of the number (M) of optical outputs of theplanar lightwave circuit.
 8. The multi-wavelength source as recited inclaim 7, wherein the optical fiber alignment device is configured toreceive the number (M) of optical fibers.
 9. The multi-wavelength sourceas recited in claim 8, wherein the optical fiber alignment device is av-groove array that includes the number (M) of v-grooves.
 10. Themulti-wavelength source as recited in claim 7, wherein the laser arraychip includes a first alignment laser configured and connected toprovide continuous wave laser light to a first alignment optical outputon the laser array chip, the first alignment optical output facingtoward the second area, the first alignment optical output positioned ata first side of the number (N) of distributed feedback lasers, whereinthe laser array chip includes a first alignment photodetector opticallyconnected to a first alignment optical input on the laser array chip,the first alignment optical input facing toward the second area, thefirst alignment optical input positioned next to the first alignmentoptical output, wherein the planar lightwave circuit includes a firstalignment waveguide configured to extend from a first alignment opticalinput on the planar lightwave circuit to a first alignment opticaloutput on the planar lightwave circuit, such that light entering thefirst alignment optical input on the planar lightwave circuit isconveyed through the first alignment waveguide and through the firstalignment optical output on the planar lightwave circuit, both the firstalignment optical input and the first alignment optical output of theplanar lightwave circuit facing toward the first area, and wherein theplanar lightwave circuit is properly aligned with the laser array chipwhen the first alignment optical input of the planar lightwave circuitis aligned with the first alignment optical output of the laser arraychip and when the first alignment optical output of the planar lightwavecircuit is aligned with the first alignment optical input of the laserarray chip, such that continuous wave laser light transmitted from thefirst alignment laser travels through the first alignment waveguide andback into the laser array chip for detection by the first alignmentphotodetector.
 11. The multi-wavelength source as recited in claim 10,wherein the laser array chip includes a second alignment laserconfigured and connected to provide continuous wave laser light to asecond alignment optical output on the laser array chip, the secondalignment optical output facing toward the second area, the secondalignment optical output positioned at a second side of the number (N)of distributed feedback lasers, wherein the laser array chip includes asecond alignment photodetector optically connected to a second alignmentoptical input on the laser array chip, the second alignment opticalinput facing toward the second area, the second alignment optical inputpositioned next to the second alignment optical output, wherein theplanar lightwave circuit includes a second alignment waveguideconfigured to extend from a second alignment optical input on the planarlightwave circuit to a second alignment optical output on the planarlightwave circuit, such that light entering the second alignment opticalinput on the planar lightwave circuit is conveyed through the secondalignment waveguide and through the second alignment optical output onthe planar lightwave circuit, both the second alignment optical inputand the second alignment optical output of the planar lightwave circuitfacing toward the first area, and wherein the planar lightwave circuitis properly aligned with the laser array chip when the second alignmentoptical input of the planar lightwave circuit is aligned with the secondalignment optical output of the laser array chip and when the secondalignment optical output of the planar lightwave circuit is aligned withthe second alignment optical input of the laser array chip, such thatcontinuous wave laser light transmitted from the second alignment lasertravels through the second alignment waveguide and back into the laserarray chip for detection by the second alignment photodetector.
 12. Themulti-wavelength source as recited in claim 1, wherein the laser arraychip is flip-chip connected to the first area using a ball grid array orcontrolled collapse chip connection bumps.
 13. The multi-wavelengthsource as recited in claim 12, wherein the substrate includes aplurality of electrically conductive structures electrically connectedto a plurality of electrically conductive pads exposed within the firstarea, the plurality of electrically conductive pads configured toreceive the ball grid array.
 14. The multi-wavelength source as recitedin claim 13, further comprising: an epoxy underfill material disposedwithin the first area between the laser array chip and the substrate andbetween solder balls of the ball grid array, wherein the trenchfacilitates deposition of the epoxy underfill material.
 15. Themulti-wavelength source as recited in claim 14, further comprising: anindex-matched epoxy material disposed between the planar lightwavecircuit and the substrate, the index-matched epoxy material disposed tofill the trench and a gap between the laser array chip and the planarlightwave circuit, the index-matched epoxy material further disposedbetween the optical fiber alignment device and the substrate, theindex-matched epoxy material disposed to fill a gap between the planarlightwave circuit and the optical fiber alignment device.
 16. Themulti-wavelength source as recited in claim 15, further comprising: astiffener structure disposed on the substrate to extend around a unionof the first area and the second area without encroaching within thethird area, the stiffener structure having a top surface at asubstantially same elevation above the substrate as a top surface of thelaser array chip; a thermal interface material disposed across topsurfaces of the stiffener structure, the laser array chip, and theplanar lightwave circuit; and a lid structure disposed on the thermalinterface material, the lid structure configured to cover the laserarray chip and the planar lightwave circuit, the lid structure alsoconfigured to extend over the stiffener structure.
 17. Themulti-wavelength source as recited in claim 1, wherein the laser arraychip and the planar lightwave circuit are collectively configured toprovide for active alignment of the planar lightwave circuit to thelaser array chip through operation of the laser array chip after thelaser array chip is disposed in the first area of the substrate.
 18. Amethod for manufacturing a multi-wavelength source, comprising: forminga substrate to include a first area for receiving a chip; forming thesubstrate to include a second area elevated relative to the first area;forming the substrate to include a trench between the first area and thesecond area, the trench having a bottom at a lower elevation within thesubstrate than the first area; forming the substrate including a thirdarea next to the second area, the third area having a lower elevationwithin the substrate than the second area; disposing a laser array chipin the first area, such that optical outputs of the laser array chipface toward the second area; disposing a planar lightwave circuit in thesecond area, such that optical inputs of the planar lightwave circuitface toward and align with respective optical outputs of the laser arraychip, and such that optical outputs of the planar lightwave circuit facetoward the third area; and disposing an optical fiber alignment devicein the third area, the optical fiber alignment device configured toreceive a number of optical fibers such that optical cores of the numberof optical fibers respectively align with the optical outputs of theplanar lightwave circuit.
 19. The method as recited in claim 18, whereinthe substrate is formed of a dielectric material.
 20. The method asrecited in claim 18, wherein the substrate is formed of aluminum oxide,or aluminum nitride, or a ceramic material.
 21. The method as recited inclaim 18, wherein the trench is formed to extend along a full length ofa side of the laser array chip that faces toward the planar lightwavecircuit.
 22. The method as recited in claim 18, wherein the laser arraychip includes a number (N) of distributed feedback lasers, wherein N isgreater than one, each of the number (N) of distributed feedback lasersconfigured to generate a different wavelength of continuous wave laserlight, each of the number (N) of distributed feedback lasers opticallyconnected to transmit the different wavelength of continuous wave laserlight to a respective optical output of the laser array chip, such thateach optical output of the laser array chip outputs one uniquewavelength of continuous wave laser light.
 23. The method as recited inclaim 22, wherein the laser array chip includes the number (N) ofsemiconductor optical amplifiers respectively optically connected to thenumber (N) of distributed feedback lasers, each of the number (N) ofsemiconductor optical amplifiers configured to generate an amplifiedversion of the continuous wave laser light received from the respectiveone of the number (N) of distributed feedback lasers and provide theamplified version of the continuous wave laser light to the respectiveoptical output of the laser array chip.
 24. The method as recited inclaim 22, wherein the planar lightwave circuit has the number (N) ofoptical inputs, wherein the method includes positioning the planarlightwave circuit so that the number (N) of optical inputs of the planarlightwave circuit respectively receive continuous wave laser light fromthe number (N) of optical outputs of the laser array chip, such thateach of the number (N) of optical inputs of the planar lightwave circuitreceives a different wavelength of continuous wave laser light, whereinthe planar lightwave circuit has a number (M) of optical outputs, theplanar lightwave circuit configured to distribute a portion of thecontinuous wave laser light received at each of the optical inputs ofthe planar lightwave circuit to each of the number (M) of opticaloutputs of the planar lightwave circuit, such that the differentwavelengths of continuous wave laser light received through the number(N) of optical inputs of the planar lightwave circuit are collectivelytransmitted through each of the number (M) of optical outputs of theplanar lightwave circuit.
 25. The method as recited in claim 24, whereinthe optical fiber alignment device is configured to receive the number(M) of optical fibers.
 26. The method as recited in claim 25, whereinthe optical fiber alignment device is a v-groove array that includes thenumber (M) of v-grooves.
 27. The method as recited in claim 24, whereinthe laser array chip includes a first alignment laser configured andconnected to provide continuous wave laser light to a first alignmentoptical output on the laser array chip, the first alignment opticaloutput on the laser array chip positioned at a first side of the number(N) of distributed feedback lasers, the method including positioning ofthe laser array chip on the substrate so that the first alignmentoptical output on the laser array chip faces toward the second area,wherein the laser array chip includes a first alignment photodetectoroptically connected to a first alignment optical input on the laserarray chip, the first alignment optical input on the laser array chippositioned next to the first alignment optical output on the laser arraychip, the method including positioning of the laser array chip on thesubstrate so that the first alignment optical input on the laser arraychip faces toward the second area, wherein the planar lightwave circuitincludes a first alignment waveguide configured to extend from a firstalignment optical input on the planar lightwave circuit to a firstalignment optical output on the planar lightwave circuit, such thatlight entering the first alignment optical input on the planar lightwavecircuit is conveyed through the first alignment waveguide and throughthe first alignment optical output on the planar lightwave circuit, themethod including positioning of the planar lightwave circuit on thesubstrate so that both the first alignment optical input on the planarlightwave circuit and the first alignment optical output on the planarlightwave circuit face toward the first area, wherein the methodincludes operating the first alignment laser to transmit continuous wavelaser light through the first alignment optical output on the laserarray chip, wherein the method includes operating the first alignmentphotodetector to detect when the continuous wave laser light enters thefirst alignment optical input on the laser array chip, and wherein themethod includes aligning the planar lightwave circuit on the substraterelative to the laser array chip so that the continuous wave laser lighttransmitted through the first alignment optical output on the laserarray chip enters the first alignment optical input on the planarlightwave circuit and travels through the first alignment waveguide toexit the first alignment optical output on the planar lightwave circuitand enter the first alignment optical input on the laser array chip andbe detected by the first alignment photodetector.
 28. The method asrecited in claim 27, wherein the laser array chip includes a secondalignment laser configured and connected to provide continuous wavelaser light to a second alignment optical output on the laser arraychip, the second alignment optical output on the laser array chippositioned at a second side of the number (N) of distributed feedbacklasers, the method including positioning of the laser array chip on thesubstrate so that the second alignment optical output on the laser arraychip faces toward the second area, wherein the laser array chip includesa second alignment photodetector optically connected to a secondalignment optical input on the laser array chip, the second alignmentoptical input on the laser array chip positioned next to the secondalignment optical output on the laser array chip, the method includingpositioning of the laser array chip on the substrate so that the secondalignment optical input on the laser array chip faces toward the secondarea, wherein the planar lightwave circuit includes a second alignmentwaveguide configured to extend from a second alignment optical input onthe planar lightwave circuit to a second alignment optical output on theplanar lightwave circuit, such that light entering the second alignmentoptical input on the planar lightwave circuit is conveyed through thesecond alignment waveguide and through the second alignment opticaloutput on the planar lightwave circuit, the method including positioningof the planar lightwave circuit on the substrate so that both the secondalignment optical input on the planar lightwave circuit and the secondalignment optical output on the planar lightwave circuit face toward thefirst area, wherein the method includes operating the second alignmentlaser to transmit continuous wave laser light through the secondalignment optical output on the laser array chip, wherein the methodincludes operating the second alignment photodetector to detect when thecontinuous wave laser light enters the second alignment optical input onthe laser array chip, and wherein the method includes aligning theplanar lightwave circuit on the substrate relative to the laser arraychip so that the continuous wave laser light transmitted through thesecond alignment optical output on the laser array chip enters thesecond alignment optical input on the planar lightwave circuit andtravels through the second alignment waveguide to exit the secondalignment optical output on the planar lightwave circuit and enter thesecond alignment optical input on the laser array chip and be detectedby the second alignment photodetector.
 29. The method as recited inclaim 18, wherein disposing the laser array chip in the first areaincludes flip-chip connecting of the laser array chip to the substrateusing a ball grid array or controlled collapse chip connection bumps.30. The method as recited in claim 29, wherein the substrate includes aplurality of electrically conductive structures electrically connectedto a plurality of electrically conductive pads exposed within the firstarea, wherein the method includes disposing the ball grid array on theplurality of electrically conductive pads.
 31. The method as recited inclaim 30, further comprising: disposing an epoxy underfill materialwithin the first area between the laser array chip and the substrate andbetween solder balls of the ball grid array; and using the trench tofacilitate deposition of the epoxy underfill material.
 32. The method asrecited in claim 31, further comprising: disposing an index-matchedepoxy material between the planar lightwave circuit and the substrate;disposing the index-matched epoxy material to fill the trench and a gapbetween the laser array chip and the planar lightwave circuit; disposingthe index-matched epoxy material between the optical fiber alignmentdevice and the substrate; and disposing the index-matched epoxy materialto fill a gap between the planar lightwave circuit and the optical fiberalignment device.
 33. The method as recited in claim 32, furthercomprising: attaching a stiffener structure to the substrate, thestiffener structure configured to extend around a union of the firstarea and the second area without encroaching within the third area, thestiffener structure having a top surface at a substantially sameelevation above the substrate as a top surface of the laser array chip;disposing a thermal interface material across top surfaces of thestiffener structure, the laser array chip, and the planar lightwavecircuit; and positioning a lid structure on the thermal interfacematerial, the lid structure configured to cover the laser array chip andthe planar lightwave circuit, the lid structure also configured toextend over the stiffener structure.
 34. The method as recited in claim18, wherein the laser array chip and the planar lightwave circuit arecollectively configured to provide for active alignment of the planarlightwave circuit to the laser array chip through operation of the laserarray chip, wherein the method includes operating the laser array chipto perform active alignment of the planar lightwave circuit to the laserarray chip after the laser array chip is disposed in the first area andconnected to the substrate.